Can stand the heat – ecology of the potentially invasive ascidian Styela plicata along the Mediterranean coast of Israel

Introduction: Both colonial and solitary ascidians (Chordata, Ascidiacea) have been gathering attention due to their impact on coastal environments. The solitary ascidian Styela plicata was first observed along the coast of Israel in 2014. It is considered a cosmopolitan species of unknown origin, and is well-known for its ability to create large aggregations on artificial substrates in the western Mediterranean Sea, North-Pacific Ocean and the Atlantic. The extreme environmental conditions that characterize the Mediterranean coast of Israel, with a salinity of 40 psu and sea-surface temperature reaching 33°C, may however present a barrier to its future spread. Methods: We examined the seasonal reproduction patterns and population structure of three populations over two years, in addition to spatial surveys and monitoring oocyte release under laboratory conditions. Results: Histological sections revealed significant differences in reproduction patterns between seasons and sites, with a higher proportion of the larger oocytes size group observed during the winter for all sites. Along the Israeli coast, with the exception of one site, S. plicata is currently restricted to marinas and ports. Discussion: With an impressive ability to survive the extreme environmental conditions and sustain reproductive populations. Acquiring data on its spread and establishment is essential for modeling S. plicata’s distribution under the current and predicted global climate changes, and for developing tools for its mitigation and control.